The present invention relates to fiber optic networks, and more particularly to light sources in a fiber optic network.
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. In response to the demand for ever higher capacity fiber optic networks, network components are designed to provide greater and greater information carrying capacity. This increases the need for greater numbers of information-carrying channels (e.g. xe2x80x9cwavelengthsxe2x80x9d) within the network. As the number of wavelengths increases, so does the demand on the number of lasers required to maintain a laser source system in a network.
FIG. 1 illustrates one type of conventional laser source system for a fiber optic network. Assume that a fiber optic network or cable comprises ten wavelength division multiplexer (WDM) systems 102a-102j. Each system comprises n wavelengths. Each xe2x80x9cwavelengthxe2x80x9d corresponds to a respective information-carrying channel wherein each channel comprises a restricted range or band of wavelengths. Each channel carries a respective signal. One laser light source is used for each wavelength in a system. Thus, for n wavelengths in system 102a, n lasers 104.1-104.n are required; for n wavelengths in system 102b, n lasers 106.1-106.n are required; and for n wavelengths in system 102j, n lasers 108.1-108.n are required. For example, if each system comprises 64 wavelengths, with ten systems, the fiber optic network requires 640 lasers.
As information carried over optical networks increases, the channels are spaced more closely (in wavelength) and therefore the pass bands of the channels become narrower, placing more stringent requirements on the lasers"" wavelength precision. Instability and imprecision can be caused by drift, mode hopping, and crosstalk, for example. Drift refers to the difference between an actual wavelength and the nominal center wavelength of the respective channel. If drift occurs, crosstalk between channels will be too large. Crosstalk occurs when one channel or part of a channel appears as noise on another channel adjacent to it. By using one laser per wavelength per system, each laser may be designed to provide a particular wavelength in a very stable manner with uniform intensity. However, lasers are expensive and the requirement of one laser per wavelength per system burdens the network operator with high costs. Also, with so many lasers in different locations, maintenance and service of the lasers are expensive and time consuming.
One conventional way of decreasing this burden is illustrated in FIG. 2. FIG. 2 illustrates a centralized laser source transmission system 200. In the system 200, one high powered laser is used for each wavelength. The optical power from each laser is delivered to a respective one of the output lines 205.1-205.n and then is split among the systems in the network. For example, assume the network has ten WDM systems 202a-202j, each comprising n wavelengths. For n wavelengths, n lasers 204.1-204.n are used, each emitting a single wavelength at ten times the power normally required for a single system. For instance, laser 204.1 emits light at wavelength xcex1, laser 204.2 emits light at wavelength xcex2, etc. The wavelength xcex1 from laser 204.1 is split ten ways among the systems 202a 202j. The same is true for the wavelengths xcex2-xcexn from lasers 204.2-204.n. The n wavelengths delivered to each of the systems 202a-202j are modulated, are multiplexed by a respective wavelength division multiplexer (MUX) 210a-210j and then are output via a respective one of the output fiber optic lines 212a-212j. Thus, for systems comprising 64 wavelengths each, instead of requiring 640 lasers as with the network illustrated in FIG. 1, the network in FIG. 2 only requires 64 lasers. Although this reduces the cost for lasers, there is a cost involved in providing high powered wavelengths. The maintenance and service of this number of single wavelength lasers is still costly and time consuming.
Accordingly, there exists a need for a multi-wavelength light source for an optical network. The light source should not compromise the stability of the wavelengths. It should reduce the costs of operating and maintaining the network. The present invention addresses such a need.
The present invention provides a method and system for providing a light source in an optical network. The method includes providing a multiple-wavelength light, and filtering the multiple-wavelength light into a plurality of separated wavelength bands for a plurality of channels. In the preferred embodiment, each of the separated wavelength bands is substantially centered about the wavelength of a respective one of a plurality of optical channels. The plurality of separated wavelength bands is stabilized and then provided to the optical network. The light source in accordance with the method and system of the present invention is designed to only output wavelengths that correspond to optical transmission channels while eliminating the rest. It suppresses possible mode hopping, thus maintaining the power stability of all channels. Since multiple wavelengths are provided in a single light source, the number of light sources required to service a network can be dramatically reduced, increasing efficiency and reducing the cost of equipment and time for maintenance as well.